Vehicle mounted cranes have become increasingly popular in recent years. Conventionally, they are mounted on the bed of a truck adjacent one end or another and are employed for loading and unloading any of a wide variety of material to and from the truck.
Typical usages include the transportation of building materials such as pallets of construction supplies, large and/or heavy conduits and the like.
Such cranes are also employed to do jobs in addition to loading and unloading functions. For example, they are frequently employed in connection with the servicing of tires for off-the-road vehicles. See, for example, commonly assigned Francis L. Zrostlik U.S. Pat. No. 3,927,778 issued Dec. 23, 1975 and Francis L. Zrostlik et al. U.S. Pat. No. 4,314,597 issued on Feb. 9, 1982.
Wherever possible, it is highly desirable that a crane that is to be mounted on a vehicle be such that it can be configured to a stowed position which will fit inside the envelope of the vehicle as, for example, the envelope defined by the cab and the bed. One crane meeting this objective is disclosed in commonly assigned Larry J. Hejlik U.S. Pat. No. 4,623,067 issued Nov. 18, 1986, the details of which are incorporated by reference. In constructions of this sort, the crane will typically include a base which is adapted to be mounted on the vehicle frame or the bed thereof. A mast is pivoted to the base for movement between an elevated position and a lowered or stowed or collapsed position. In the elevated position, a boom is moved relative to the mast and is provided with sufficient height to accomplish its intended purpose. When the vehicle is in transit, however, it is desirable to maintain the entire crane within the vehicle envelope as alluded to previously and accordingly, the mast will be moved to a collapsed or stowed position. This in turn lowers the height of the boom to bring it within the envelope of the vehicle.
In certain cranes of this type, particularly those having telescoping booms which overly the mast when in the collapsed position as opposed to those having articulated booms, when the mast is moved to its elevated position by pivoting about a horizontal axis, the resulting movement tends to pivot the end of the boom downwardly into the vehicle frame. If the operator is not careful, it is possible to damage the crane when the end of the boom undesirably comes into contact with the vehicle frame or truck bed. Damage to the vehicle could also result.
In order to avoid this possibility, in prior art cranes of this sort, it has been necessary to operate two controls substantially simultaneously. One control is that used to control a motor, usually a hydraulic cylinder, employed to elevate the mast relative to the base. The second control is for a motor, again usually a hydraulic cylinder, that is utilized to change the attitude of the boom relative to the mast so that the end of the boom will not move downwardly as the mast is being elevated.
Proper usage of the two controls substantially simultaneously takes dexterity and alertness on the part of the operator; if not performed properly, damage as mentioned previously can result.
The present invention is directed to overcoming one or more of the above problems.